Shoe and the same for swash plate type compressor

ABSTRACT

A shoe for use in a swash plate type compressor, interposed between a swash plate and a piston, has a plane sliding surface, a spherical sliding surface and a side surface. The plane sliding surface, which is substantially a plane, slides with respect to the swash plate. The spherical sliding surface, which is substantially a part of sphere surface, slides with respect to the piston. The side surface is provided between the plane sliding surface and the spherical sliding surface. The side surface includes a chamfered surface adjacent to the plane sliding surface. An angle between the chamfered surface and the extended plane sliding surface ranges from 20° to 80°.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a shoe for use in a swash platetype compressor and a swash plate type compressor with the pair of shoesinterposed between a swash plate and a piston.

[0002] A swash plate type compressor compresses gas by convertingrotation of a swash plate to reciprocation of a piston. A pair of shoes,or sliding members, is interposed between the swash plate, which rotatesat a high speed, and the piston, which reciprocates at a high speed, toensure smooth operations of the swash plate and the piston. Since theswash plate rotates at a high speed, sliding performance between theswash plate and the piston is required to be relatively high. The shoeis generally hemispherical crown-shaped. Namely, the shoe includes asubstantially plane sliding surface sliding with respect to the swashplate, and a substantially hemispherical sliding surface sliding withrespect to the piston. In the hemispherical crown shoe, it is desiredthat sliding performance between the plane sliding surface and a slidingsurface of the swash plate is relatively high. Lubricant oil is suppliedbetween the sliding surfaces, and a layer of the lubricant oil is formedbetween the sliding surfaces. Thereby, relatively high slidingperformance is maintained. Accordingly, when the lubricant oil suppliedbetween the sliding surfaces is not sufficient, sliding performancetherebetween deteriorates.

[0003] A prior art for supplying sufficient lubricant oil between thesliding surface of the hemispherical crown shoe and the sliding surfaceof the swash plate is disclosed in Japanese Unexamined PatentPublication No.56-126686. In the prior art, a chamfered surface isprovided in the vicinity of the plane sliding surface of the shoe withrespect to the swash plate, and an angle between the chamfered surfaceand the extended plane sliding surface of the shoe with respect to theswash plate ranges from 0.5° to 10°. According to the prior art,sufficient lubricant oil is supplied between the sliding surfaces due tothe chamfered surface provided at the outer periphery of the shoe.

[0004] There is another problem that causes sliding performance todeteriorate. For example, There are many foreign substances in a swashplate type compressor, such as refuse produced due to friction invarious places, remaining microscopic burrs arisen upon manufacturingprocess of components, and dusts introduced from a refrigerant conduitconnected to the compressor. These foreign substances should besufficiently managed. However, completely removing these foreignsubstances is difficult. Therefore, these foreign substances can beinvolved in between the sliding surfaces, and then can remain. When theforeign substances remain between the sliding surfaces, the slidingsurfaces are flawed, and sliding performance between the slidingsurfaces deteriorates. When the angle between the chamfered surface andthe extended plane sliding surface of the shoe with respect to the swashplate is as small as that in the prior art, not only lubricant oil butalso foreign substances can be involved in between the sliding surfaces.Actually, sufficient sliding performance has not been obtained by suchthe hemispherical crown shoe yet.

SUMMARY OF THE INVENTION

[0005] The present invention addresses the above-mentioned problems byproviding an improved shoe that ensures relatively high slidingperformance.

[0006] According to the present invention, a shoe for use in a swashplate type compressor, interposed between a swash plate and a piston,has a plane sliding is surface, a spherical sliding surface and a sidesurface. The plane sliding surface, which is substantially a plane,slides with respect to the swash plate. The spherical sliding surface,which is substantially a part of sphere surface, slides with respect tothe piston. The side surface is provided between the plane slidingsurface and the spherical sliding surface. The side surface includes achamfered surface adjacent to the plane sliding surface. An anglebetween the chamfered surface and the extended plane sliding surfaceranges from 20° to 80°.

[0007] The present invention also provides a swash plate type compressorhaving a housing, a drive shaft, a swash plate, a piston and a shoe. Thedrive shaft is rotatably supported by the housing. The swash plate isoperatively connected to the drive shaft. The piston is accommodated inthe housing, and is operatively connected to the swash plate. The shoeis interposed between the swash plate and the piston. The shoe includesa plane sliding surface, a spherical sliding surface and a side surface.The plane sliding surface, which is substantially a plane, slides withrespect to the swash plate. The spherical sliding surface, which issubstantially a part of sphere surface, slides with respect to thepiston. The side surface is provided between the plane sliding surfaceand the spherical sliding surface. The side surface includes a chamferedsurface adjacent to the plane sliding surface. An angle between thechamfered surface and the extended plane sliding surface ranges from 20°to 80°.

[0008] Other aspects and advantages of the invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The features of the present invention that are believed to benovel are set forth with particularity in the appended claims. Theinvention together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

[0010]FIG. 1 is a longitudinal cross-sectional view of a swash platetype compressor provided with a pair of shoes according to an embodimentof the present invention;

[0011]FIG. 2 is an enlarged cross-sectional view of one of the pair ofshoes in FIG. 1;

[0012]FIG. 3 is an enlarged partially cross-sectional view of one of thepair of shoes sliding with respect to the swash plate according to theembodiment;

[0013]FIG. 4 is an enlarged partially cross-sectional view of one of thepair of shoes sliding with respect to the swash plate, and a foreignsubstance involved in between the shoe and the swash plate;

[0014]FIG. 5 is a table of the diameter q of a foreign substance, theradius r of curvature of a rounded corner and a tangent plane angle βduring times when a foreign substance is in contact with the roundedcorner;

[0015]FIG. 6A is a partial end view of a shoe according to anotherembodiment of the present invention;

[0016]FIG. 6B is a partial end view of a shoe according to anotherembodiment of the present invention;

[0017]FIG. 7 is a schematic view of a process for boring a recess;

[0018]FIG. 8 is a schematic view of a process for forging a shoe;

[0019]FIG. 9A is a partially cross-sectional view of a shoe #1 fordurability test against cast iron particles;

[0020]FIG. 9B is a partially cross-sectional view of other shoes #2 to#4 for durability test against cast iron particles;

[0021]FIG. 9C is a partially cross-sectional view of the other shoe #5for durability test against cast iron particles;

[0022]FIG. 10 is a schematic view of durability test against cast ironparticles;

[0023]FIG. 11 is a graph of the number of flaws and the depth of thedeepest flaw as a function of the diameter of cast iron particles, thediameter of which range from 38 μm to 75 μm according to the durabilitytest; and

[0024]FIG. 12 is a graph of the number of flaws and the depth of thedeepest flaw as a function of the diameter of cast iron particles, thediameter of which range from 38 μm to 75 μm according to the durabilitytest.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] An embodiment of the present invention will now be described withreference to FIGS. 1 to 12. A pair of shoes constituting a swash platetype compressor for use in an air conditioner of a vehicle will bedescribed, for example. The front side and the rear side correspond tothe left side and the right side in FIG. 1, respectively.

[0026] As shown in FIG. 1, the reference numeral 10 denotes a cylinderblock, and a plurality of cylinder bores 12 is defined in the cylinderblock 10 on an identical circumference relative to the central axis ofthe cylinder block 10. The cylinder bores 12 extend in the direction ofthe central axis of the cylinder block 10 The cylinder bores 12 eachaccommodates a single-headed piston 14 so as to reciprocate. The frontend surface of the cylinder block 10 connects with a front housing 16,and the rear end surface of the cylinder block 10 connects with a rearhousing 18 through a valve plate assembly 20. The front housing 16, therear housing 18 and the cylinder block 10 constitute a housing of theswash plate type compressor. A suction chamber 22 and a dischargechamber 24 are defined between the rear housing 18 and the valve plateassembly 20, and connect with an external refrigerant circuit, which isnot shown, through an inlet 26 and an outlet 28, respectively. The valveplate assembly 20 forms a suction port 32, a suction valve 34, adischarge port 36 and a discharge valve 38.

[0027] A drive shaft 50 is supported by the housing so as to rotate withrespect to the central axis of the cylinder block 10. The front housing16 and the cylinder block 10 respectively support the front end and therear end of the drive shaft 50 through bearings. The cylinder block 10forms a support hole 56 along its central axis, and the rear end of thedrive shaft 50 is supported by the support hole 56. The front end of thedrive shaft 50 connects with an engine of a vehicle, or a drivingsource, which is not shown, through a clutch mechanism such as anelectromagnetic clutch. Therefore, as the drive shaft 50 connects withthe engine by the clutch mechanism upon an operation of the engine, thedrive shaft 50 rotates around the axis thereof.

[0028] A swash plate 60 is operatively connected to the drive shaft 50such that the swash plate 60 tilts and relatively moves in a directionalong the axis of the drive shaft 50. The swash plate 60 forms a throughhole 61 along its central axis, and the drive shaft 50 extends throughthe through hole 61. The through hole 61 gradually increases in diametertoward both opening ends of the through hole 61, and the cross sectionsof the opening ends are oblong holes. A lug plate 62 is secured to thedrive shaft 50, and is supported by the front housing 16 through athrust bearing 64. The swash plate 60 integrally rotates with the driveshaft 50 and tilts with respect to the axis of the drive shaft 50through a hinge mechanism 66. The hinge mechanism 66 is constituted of apair of support arms 67 fixed to the lug plate 62, a pair of guide pins69 slidably fitted into a pair of guide holes 68 of the support arms 67,the through hole 61 of the swash plate 60, and the outer circumferentialsurface of the drive shaft 50.

[0029] The piston 14 includes an engaging portion 70 and a head 72. Theengaging portion 70 overpasses the periphery of the swash plate 60. Thehead 72 formed with the engaging portion 70 is fitted into the cylinderbore 12. The head 72 in the present embodiment is a hollow head to belight in weight. The head 72, the cylinder bore 12 and the valve plateassembly 20 cooperatively define a compression chamber. Also, theengaging portion 70 engages with the periphery of the swash plate 60through a pair of shoes 76, which is substantially hemispherical. Theshoes 76 will be described later.

[0030] Rotation of the swash plate 60 is converted to reciprocation ofthe piston 14. As the piston 14 moves from a top dead center toward abottom dead center, refrigerant gas in the suction chamber 22 is suckedinto the compression chamber in the cylinder bore 12 through the suctionport 32 and the suction valve 34. As the piston 14 moves from the bottomdead center toward the top dead center, the refrigerant gas in thecompression chamber in the cylinder bore 12 is compressed and dischargedto the discharge chamber 24 through the discharge port 36 and thedischarge valve 38. Compression reactive force acts on the piston 14 ina direction along the axis of the drive shaft 50 in accordance withcompressing the refrigerant gas. The front housing 16 receives thecompression reactive force through the piston 14, the swash plate 60,the lug plate 62 and the thrust bearing 64.

[0031] The cylinder block 10 forms a supply passage 80 so as to extendthrough the cylinder block 10. The supply passage 80 interconnects thedischarge chamber 24 and a crank chamber 86, which is defined betweenthe front housing 16 and the cylinder block 10. A control valve 90 isinterposed in the supply passage 80. The value of an electric currentsupplied to a solenoid 92 of the control valve 90 is controlled by acontroller mainly constituted of a computer, which is not shown, basedon information such as cooling load.

[0032] The drive shaft 50 forms a bleed passage 100 inside. The bleedpassage 100 opens its one end to the support hole 56, and opens itsother end to the crank chamber 86. The support hole 56 interconnectswith the suction chamber 22 through a bleed port 104.

[0033] The swash plate type compressor in the present embodiment is avariable displacement type. The pressure in the crank chamber 86 iscontrolled by utilizing pressure differential between the dischargechamber 24 as a relatively high pressure region and the suction chamber22 as a relatively low pressure region. Thereby, pressure differentialbetween the pressure in the compression chamber in the cylinder bore 12applied to the pistons 14 and the pressure in the crank chamber 86 isadjusted, and strokes of the pistons 14 are varied by varying theinclination angle of the swash plate 60, thus adjusting the displacementof the compressor. Additionally, the crank chamber 86 disconnects fromthe discharge chamber 24 by energizing the control valve 90, and thecrank chamber 86 interconnects with the discharge chamber 24 byde-energizing the control valve 90. Thereby, the pressure in the crankchamber 86 is controlled.

[0034] The cylinder block 10 and the pistons 14 are made of aluminumalloy. The outer circumferential surfaces of the pistons 14 are coatedwith fluororesin. Since the pistons 14 are coated with fluororesin,seizure is inhibited by avoiding directly contacting with a metal of thesame kind, and clearances between the cylinder block 12 and the pistons14 are drastically reduced. Besides, the material of the cylinder block10, the pistons 14 and the coating layers are not limited as describedabove, but may be changed into other materials.

[0035] The engaging portions 70 of the pistons 14 are substantiallyU-shaped. The engaging portions 70 each provide a pair of arms 120, 122and a connecting portion 124. The pair of arms 120, 122 extends inparallel with each other in a direction perpendicular to the centralaxis of the head 72. The connecting portion 124 interconnects the basesof the arms 120, 122. The facing surfaces of the arms 120, 122 formspherical concave surfaces 128 for supporting the shoes 76 and slidingwith respect to the shoes 76, respectively. The spherical concavesurfaces 128 cooperatively form a part of an identical hypotheticalspherical sliding surface.

[0036] The swash plate 60, which slides with respect to the shoes 76, ismade of ductile iron FCD700. Aluminum layers are formed on the slidingsurfaces 132, 134 of the base member by metal spraying, and lubricantlayers are further formed on the aluminum layers. The lubricant layersare made of synthetic resin dispersedly containing molybdenum disulfideand graphite as a solid lubricant. The aluminum layers sufficientlyreduce friction generated between the sliding surfaces, and ensurerelatively high sliding performance between the shoes 76 and the swashplate 60. Even if the lubricant layers abrade or peel off due to somecauses, the aluminum layers inhibit the base member from directlysliding, and maintain a smooth slide. In the swash plate 60, thethickness of the lubricant layers are respectively 15 μm, and thethickness of the aluminum layers are respectively 60 μm. Besides, Thestructure of the swash plate 60, such as the material of the base memberof the swash plate 60, the material and thickness of the lubricantlayer, with or without the lubricant layer, the thickness of thealuminum spraying layer, and with or without the aluminum sprayinglayer, may be varied. Since an iron series material is relatively lowcost, a compressor with a swash plate made of iron series is alsorelatively low cost. In addition, when operating the compressor withconstant displacement, the inclination angle of the swash plate isdesired to be constant. Since the swash plate made of iron series isrelatively large in weight, the inclination angle of the swash plate canbe stable due to its inertial force. Since the shape of the swash platemade of iron series is complicated, the swash plate is preferablymanufactured by molding. Therefore, the material of the swash plate ispreferably cast iron, and is more preferably ductile cast iron havingrelatively high strength and high durability, and is much morepreferably FCD700 having further high strength. Since the swash platerotates at a high speed, the swash plate and the shoes slide underrelatively hard conditions. Therefore, the lubricant layer is formed onthe sliding surface of the swash plate for ensuring lubrication betweenthe sliding surfaces. Thereby, friction generated between the slidingsurfaces is reduced, and the compressor smoothly operates. For example,the lubricant layer may be formed by synthetic resin containing a solidlubricant. In such a state, the solid lubricant includes at least one ofmolybdenum disulfide, boron nitride, tungsten disulfide, graphite andpolytetrafluoroethylene. Also, the synthetic resin includes at least oneof polyamideimide, epoxy resin, polyether ketone and phenolic resin. Forexample, synthetic resin layer dispersedly containing the solidlubricant is formed on the surface of the swash plate by spraying, andafter that the synthetic resin layer is solidified, thus forming thelubricant layer. Besides, the thickness of the lubricant layerpreferably ranges from 3 μm to 30 μm. Also, the strength of thelubricant layer formed on the swash plate is less than that of the basemember of the swash plate. When the lubricant layer is removed due toabrasion or peeling, the base member directly slides with respect to theshoe. Thereby, sliding performance of the swash plate deteriorates. Whenthe base member of the swash plate abrades due to a direct slide,sliding performance of the swash plate further deteriorates. Therefore,even if the lubricant layers are removed off, the shoes including metalspraying layers between the base members and the lubricant layerssufficiently ensure high sliding performance due to high slidingperformance of the metal spraying layers. Additionally, when the shoesmade of iron series alloy slide with respect to the swash plate, thebase member of which is made of iron series alloy, and when thelubricant layer of the swash plate is removed off, members made ofmaterials of the same kind slide with respect to each other. Thereby,seizure may arise. Therefore, the metal spraying layer inhibits theseizure from arising. Also, an aluminum spraying layer is preferablyemployed as the metal spraying layer because of its relatively low cost.Also, the thickness of the metal spraying layer preferably ranges from100 μm to 200 μm.

[0037] As shown in FIG. 2, the shoe 76 includes a plane sliding surface136, a spherical sliding surface 138 and a side surface 140. The planesliding surface 136, which is substantially a plane in shape, slideswith respect to the swash plate 60. The spherical sliding surface 138,which is substantially a part of sphere surface in shape, slides withrespect to the piston 14. The side surface 140 interconnects the planesliding surface 136 and the spherical sliding surface 138. Strictly, theplane sliding surface 136 forms a convex surface, the radius ofcurvature of which is very large. Also, a recess 142 is formed at thecenter of the plane sliding surface 136 so as to stay lubricant oil.Thereby, high sliding performance is ensured. Consequently, the planesliding surface 136 is annular in shape. Besides, the shoe 76 isgenerally called a hemispherical crown shoe. Practically, a sphericalsliding surface and a plane sliding surface of the hemispherical crownshoe are modified from a strict spherical sliding surface and a strictplane sliding surface so as to improve sliding performance. Also,strictly, a shoe for use in a variable displacement compressor issmaller than a hemisphere, and a shoe for use in a fixed displacementcompressor is larger than a hemisphere. In the variable displacementcompressor, since both spherical sliding surfaces of the pair of shoesdisposed on each side of the swash plate are required to cooperativelyform a part of identical hypothetical spherical sliding surface, each ofthe shoes is substantially a part of sphere, and the thickness of eachof the shoe is substantially a half of the thickness of the swash plateless than a hemisphere. On the other hand, in the fixed displacementcompressor, since no such limitations as that of the variabledisplacement compressor is required, each of the shoes is substantiallya part of sphere. However, the thickness of each of the shoes is morethan a hemisphere to inhibit the area of the sliding surface of the shoefrom reducing even if the plane sliding surface abrades.

[0038] The side surface 140 adjacent to the plane sliding surface 136forms a chamfered surface 146, which is a side surface of a truncatedcone. An angle between the chamfered surface 146 and an extended planesliding surface 144 is a predetermined angle α, or a chamfered surfaceangle α in the following. In the present embodiment, the chamferedsurface angle α of the shoe 76 is 45°. is The side surface 140 otherthan the chamfered surface 146, or an upper portion relative to thechamfered surface 146 in FIG. 2, forms a rounded surface 148, the radiusof curvature of which is relatively large. The rounded surface 148interconnects the chamfered surface 146 and the spherical slidingsurface 138 without any definite border. Also, the chamfered surface 146connects with the plane sliding surface 136 through a rounded corner150. In other words, the chamfered surface 146 is adjacent to the planesliding surface 136 by sandwiching the rounded corner 150. In thepresent embodiment, the radius of curvature of the rounded corner 150 ofthe shoe 76 is 0.2 mm. Besides, a relatively small rounded corner isformed between a surface defining the recess 142 and the plane slidingsurface 136.

[0039] As shown in FIGS. 1 and 2, the spherical sliding surface 138 ofthe pair of shoes 76 is slidably supported by a sliding surface 128 ofthe piston 14. The plane sliding surface 136 of the pair of shoes 76contacts with sliding surfaces 132, 134 of the swash plate 60 at theouter peripheral portions, and the pair of shoes 76 sandwiches the swashplate 60 at the outer peripheral portions. In other words, the planesliding surfaces 136 of the shoes 76 slide with respect to the swashplate 60, and the spherical sliding surfaces 138 of the shoes 76 slidewith respect to the piston 14. Besides, the spherical sliding surfaces138 of the pair of shoes 76 cooperatively form a part of identicalhypothetical spherical sliding surface. Namely, the shoe 76 issubstantially a part of sphere, the thickness of which is about a halfof the thickness of the swash plate 60 less than a hemisphere.

[0040] The shoe 76 includes a base member 152 and a metal plating layer154, which coats the surface of the base member 152. In FIG. 2, thethickness of the metal plating layer 154 is exaggerated for easierunderstanding. The base member 152 is made of Al-Si series alloy such asA4032, the base of which is aluminum with containing silicon such thatthe composition ratio is closer to that of eutectic. The metal platinglayer 154 is formed by electroless plating with nickel. The hardness andthe strength of the metal plating layer 154 is relatively high. Thereby,the shoe 76 is inhibited from abrading and being flawed. The metalplating layer 154 includes an outer layer and an inner layer, which arenot shown in figures. The outer layer forms the surface of the shoe 76.The inner layer is interposed between the outer layer and the basemember 152. The outer layer is formed by electroless plating with nickeleutectic with phosphorus, boron and tungsten (Ni—P—B—W electrolessplating). The inner layer is formed by electroless plating with nickeleutectic with phosphorus (Ni—P electroless plating). Additionally, theaverage thickness of the outer layer is 25 μm, and the average thicknessof the inner layer is 25 μm. The total average thickness of the metalplating layer 154 is 50 μm. Besides, the material of the base member 152is not limited to that in the embodiment described above, but may bemodified into various kinds of structures. The shoe, the base member ofwhich is made of aluminum series alloy, is relatively light in weight.Therefore, the shoe is appropriate for use in a swash plate typecompressor installed to an air conditioner of a vehicle. A kind ofaluminum series alloy is not limited. Aluminum alloy, which is generallyused, or which is well-known, may be applied. Concretely, for example,Al—Si having eutectic composition of approximately A4032, may beapplied. Since Al—Si series alloy has relatively small coefficient ofthermal expansion and relatively high abrasion resistance, the shoesslide smoothly. Also, for example, Al—Cu—Mg series alloy such as A2017or A2024 may be applied. Since the strength of the Al—Cu—Mg series alloyis relatively high, the shoes perform relatively high strength and highdurability. Since the strength and the hardness of the aluminum seriesalloy are relatively low, the aluminum series alloy is easily deformed,is flawed, and is relatively low in abrasion resistance. Since the shoes76 in the present embodiment include the metal plating layer 154 on itssurface. Thereby, the shoes 76 perform relatively high abrasionresistance. Also, the shoes 76 are inhibited from being flawed due tothe metal plating layer, and have relatively high sliding performance.Besides, the metal plating layer may be formed on part of surface of theshoes, and, for example, may be formed on the plane sliding surfaceonly. Also, a kind of the metal plating layer is not limited. As far asthe metal plating layer is harder than aluminum series alloy forming thebase member of the shoes, the metal plating layer inhibits the shoesfrom being flawed. The hardness of the metal plating layer is preferablyHv300 (Vickers hardness) or above. The shoes including the metal platinglayer perform relatively high abrasion resistance, and are inhibitedfrom being flawed. Concretely, the metal plating layer may be formed byelectroless plating with nickel, a series of electroless plating withcobalt eutectic with phosphorus, and hard chrome plating. Particularly,the metal plating layer formed by Ni—P electroless plating, or byelectroless plating with nickel eutectic with boron (Ni—B electrolessplating), is uniform, and the metal plating layers when solidified hasthe hardness of Hv500 or above. Thereby, the metal plating layersperform relatively high abrasion resistance and high anti-corrosion.Therefore, the metal plating layer is preferably formed by electrolessplating with nickel. Also, the metal plating layer may be formed with asingle layer, and may be formed with a plurality of layers. For example,the metal plating layer includes an outer layer forming the surface ofthe shoe and an inner layer between the outer layer and the base member.When the two layers are formed by electroless plating with nickel,preferably, the inner layer is formed by Ni—P electroless plating, andthe outer layer is formed by Ni—P electroless plating containingrelatively small phosphorus in ratio and also containing anotherchemical element. A series of Ni—P metal plating layer firmly adheres toaluminum series alloy, solidifies relatively in a short time, materialsfor a plating bath are relatively low cost, and hardly corrodes.Therefore, the shoe having Ni—P metal plating layer also performs suchcharacteristics. Additionally, the metal plating layer formed byNi—P—B—W electroless plating performs much relatively high abrasionresistance. Therefore, the outer layer is preferably formed by Ni—P—B—Welectroless plating. Also, the metal plating layer formed by Ni—Pelectroless plating is much relatively low cost among a series ofelectroless plating with nickel, and firmly adheres to the base member.Therefore, the inner layer is preferably formed by Ni—P electrolessplating. Besides, when the metal plating layer includes the inner layerformed by a series of Ni—P electroless plating and the outer layerformed by a series of Ni—B electroless plating, the thickness of theinner layer preferably ranges from 1 μm to 25 μm, the thickness of theouter layer preferably ranges from 19 μm to 75 μm, and the totalthickness of the metal plating layer preferably ranges from 20 μm to 100μm. Also, iron series alloy is relatively low cost and relatively highin strength and hardness. Therefore, the shoe, the base member of whichis made of iron series alloy, is relatively low cost, and performsrelatively high abrasion resistance and high durability. A kind of ironseries alloy is not limited. Carbon chrome bearing steel SUJ2 ispreferably employed. The shoe made of SUJ2 is manufactured by heattreatment such as quenching or tempering.

[0041] The metal plating layer 154 of the shoe 76 and the aluminumspraying layer and the lubricant layer of the swash plate 60 are omittedin FIG. 3 for easier understanding. Strictly, the plane sliding surface136 of the shoe 76 is convex in shape as mentioned above. Therefore, asmall clearance 160 is maintained between the plane sliding surface 136of the shoe 76 adjacent to the outer periphery and the sliding surface132 or 134 of the swash plate 60. A layer of lubricant oil is formed inbetween the sliding surfaces. Thereby, sliding performance improves.Besides, the clearance 160 is exaggerated in FIG. 3. In is FIG. 3, thechamfered surface angle a between the chamfered surface 146 of the shoe76 and the extended plane sliding surface 144 is different from an anglebetween the chamfered surface 146 and the sliding surface 132 of theswash plate 60, the angle called pseudo-chamfered surface angle α′.Actually, an angle differential between the chamfered surface angle αand the pseudo-chamfered surface angle α′ is small enough, the angledifferential being exaggerated in FIG. 3. Therefore, thepseudo-chamfered surface angle α′ is regarded as approximately the sameangle as the chamfered surface α.

[0042] When the shoe 76 slides with respect to the swash plate 60, thatis, the shoe 76 relatively moves toward a direction indicated by anarrow in FIG. 3, lubricant oil on the surface of the swash plate 60 isled from a space 162 between the chamfered surface 146 of the shoe 76and the sliding surface 132 of the swash plate 60 into the clearance160. The cross section of the space 162 is wedge-shaped. Since thechamfered surface angle α and the radius of curvature of the roundedcorner 150 are appropriately designed, that is, the chamfered surfaceangle α is 45° and the radius of curvature of the rounded corner 150 is0.2 mm in the present embodiment, relatively large foreign substances164, which may affect sliding performance, is retarded from beinginvolved in the clearance 160 when the foreign substances 164 areinvolved in the space 162. Namely, when the chamfered surface angle α isappropriately designed, the foreign substances 164 are excluded.Accordingly, the shoe 76 in the present embodiment efficiently excludesforeign substances, and hardly involves the foreign substances betweenthe sliding surfaces. Thereby, high sliding performance is ensured.

[0043] The radius of curvature of the rounded corner 150 will bedescribed. FIG. 3 shows a state that one of the relatively large foreignsubstances 164 is involved in the space 162. When the radius ofcurvature of the rounded corner 150 is relatively large, and when theforeign substance 164 is relatively small, the foreign substance 164contacts with the rounded corner 150, as shown in FIG. 4. In such astate, the foreign substance 164 is excluded or involved based on anangle β or a tangent plane angle between a tangent plane 166 at a pointof contact, where the foreign substance 164 abuts the rounded corner150, and the extended plane sliding surface 144. Besides, the extendedplane sliding surface 144 is regarded as the same surface as the slidingsurface 132 of the swash plate 60. As the tangent plane angle β isrelatively large, the foreign substances 164 are easily excluded. As thetangent plane angle β is relatively small, the foreign substances 164are easily involved in between the sliding surfaces.

[0044] When the foreign substances 164 are assumed to be spheres, andwhen q denotes the diameter of the sphere, that is, the diameter offoreign substance 164, and when r denotes the radius of curvature of therounded corner 150, relationship among the tangent plane angle β, thediameter q of foreign substances 164 and the radius r of curvature ofrounded corner 150 is expressed as follows.

r−r·cosβ=q/2+(q/2)·cosβ

[0045] According to the above-described expression, the tangent planeangles β are calculated based on each diameter q of the foreignsubstances and each radius r of curvature of rounded corner 150,respectively, and are shown in FIG. 5.

[0046] As shown in FIG. 5, when the diameter q of the foreign substanceis the same, as the radius of curvature of the rounded corner 150reduces, the tangent plane angle β increases. When the radius r ofcurvature of the rounded corner 150 is the same, as the diameter q ofthe foreign substance increases, the tangent plane angle β increases.Also, in the shoe 76 described in the present embodiment, the chamferedsurface angle α is 45°, and the radius of curvature of the roundedcorner 150 is 0.2 mm. Therefore, the foreign substances 164, thediameter of which are approximately above 70 μm, contact with thechamfered surface 146, and the foreign substances 164, the diameter ofwhich are about 70 μm or below, contact with the rounded corner 150. Inthe shoe 76 described in the present embodiment, even if the foreignsubstances 164 contact with the rounded corner 150, the tangent planeangles β at points of contacts of the foreign substances 164, thediameters of which are approximately 20 μm or above, exceed 20°.Therefore, the shoe 76 in the present embodiment efficiently excludesthe foreign substances 164, the diameters of which are relatively small.

[0047] For example, when the tangent plane angle β is 20°, and when theradius of curvature of the rounded corner 150 is 0.5 mm, the shoe 76efficiently excludes the foreign substances 164, the diameters of whichare approximately 30 μm or above. Also, when the tangent plane angle βis 20°, and when the radius of curvature of the rounded corner 150 is0.3 mm, the shoe 76 efficiently excludes the foreign substances 164, thediameters of which are approximately 20 μm or above.

[0048] As the radius of curvature of the rounded corner 150 reduces, theshoe 76 excludes the foreign substances 164 more efficiently, asmentioned above. On the other hand, when the radius of curvature of therounded corner 150 is relatively large, lubricant oil is moreefficiently involved in between the sliding surfaces, as compared withthe radius of curvature of the rounded corner 150, which is relativelysmall. When the radius of curvature of the rounded corner 150 isextremely small, and when the rounded corner 150 of the shoe 76 contactswith the sliding surface 132 of the swash plate 60, the rounded corner150 of the shoe 76 may peel off the lubricant layer containing a solidlubricant because of the relatively low strength and hardness of thelubricant layer. Also, when the radius of curvature of the roundedcorner 150 is extremely small, the rounded corner 150 of the shoe 76excludes not only the foreign substances 164 but also lubricant oil.Furthermore, the surfaces of the shoes 76 are usually smoothed by barrelpolishing, and the shoes 76 may abut against each other upon barrelpolishing. Therefore, when the radius of curvature the rounded corner150 is extremely small, the shoes 76 may be flawed due to the roundedcorner 150. Accordingly, the radius of curvature of the rounded corner150 of the shoe 76 is determined based on the purpose of the shoe 76 inview of characteristics for excluding foreign substances 164 andcharacteristics for involving lubricant oil. To smoothly involve thelubricant oil in between the sliding surfaces, to inhibit the shoe frombeing flawed upon barrel polishing, and to avoid the metal plating layerfrom abrading, the radius of curvature of the rounded corner ispreferably 0.05 mm or above, and is more preferably 0.1 mm or above, andis much more preferably 0.15 mm or above. When the radius of curvatureof the rounded corner is relatively large, relatively small foreignsubstances abut not against the chamfered surface but against therounded corner. In such a state, characteristics for excluding foreignsubstances depends on an angle between a tangent plane at a point ofcontact with a foreign substance and the extended plane sliding surface,that is, a tangent plane angle. When the shoe abuts against foreignsubstances at its chamfered surface, as the tangent plane angleincreases, characteristics for excluding foreign substances improves. Inaddition, when a foreign substance of the same diameter abuts againstthe rounded corner, as the radius of curvature of the rounded cornerincreases, the tangent plane angle reduces. Namely, as the radius ofcurvature of the rounded corner reduces, characteristics for excludingforeign substances improves. When the shoe abuts against foreignsubstances at its chamfered surface, the chamfered surface angleexceeding 20° sufficiently excludes foreign substances. Likewise, whenthe shoe abuts against foreign substances at its rounded corner, thetangent plane angle exceeding 20° sufficiently excludes foreignsubstances. For example, when foreign substances are assumed to besphere in shape, and when the rounded corner having the radius ofcurvature of 0.5 mm abuts against a foreign substance having thediameter of approximately 30 μm, the tangent plane angle isapproximately 20°. Also, when the rounded corner having the radius ofcurvature of 0.3 mm abuts against a foreign substance having thediameter of approximately 20 μm, the tangent plane angle isapproximately 20°. Accordingly, when focusing on characteristics forexcluding foreign substances, the radius of curvature of the roundedcorner is 0.5 mm or below, preferably is 0.4 mm or below, and is morepreferably 0.3 mm or below.

[0049] A conventional shoe (not shown in the drawings) will be describedfor comparing the conventional shoe with the shoe 76 in the presentembodiment. A chamfered surface angle of the conventional shoe is a fewdegrees. Therefore, the conventional shoe hardly excludes foreignsubstances involved in between the sliding surfaces, and the chamferedsurface climbs on the foreign substances. Thereby, the foreignsubstances are strongly caught in between the sliding surfaces inaccordance with the movement of the conventional shoe. Namely, theforeign substances are easily involved in a space between the slidingsurfaces due to the wedge-shaped cross section of the space.Accordingly, the conventional shoe not only easily involves the foreignsubstances in between the sliding surfaces, but also causes a planesliding surface with respect to the swash plate to be severely flawed.Also, the conventional shoe may peel off the lubricant layer formed onthe sliding surface of the swash plate, and may cause the slidingsurface of the swash plate to be flawed. Consequently, the slidingperformance of the conventional shoe is not sufficient.

[0050] In the above-described shoe 76 in the present embodiment, thechamfered surface angle α is 45°, and the radius of curvature of therounded corner 150 is 0.2 mm. According to the present invention, thechamfered surface angle α and the radius of curvature of the roundedcorner 150 are determined based on the purpose of the shoe. When thechamfered surface angle α is a relatively small appropriate angle, theshoe 76 sufficiently involves lubricant oil in between the slidingsurfaces. However, as the chamfered surface angle α reduces, the shoe 76excludes foreign substance between the plane sliding surface 136 and thesliding surface of the swash plate 60 less efficiently. Namely, thechamfered surface 146 easily climbs on the foreign substances. When theshoe 76 moves in such a state, the foreign substances are consequentlyinvolved in between the plane sliding surface 136 and the slidingsurface of the swash plate 60. On the contrary, as the chamfered surfaceangle α increases, the chamfered surface 146 is operative to exclude theforeign substances. Namely, as the chamfered surface angle α increases,the chamfered surface 146 excludes foreign substance more efficiently.

[0051] When foreign substances are involved in between the slidingsurfaces, the foreign substances cause not only friction of the slidingsurfaces to increase but also each of the sliding surfaces to be flawed.The flaws on each of the sliding surfaces further flaw each of thefacing sliding surfaces, and cause sliding performance to deteriorate.When the chamfered surface angle α is relatively small, the shoe 76climbs on the foreign substances. Therefore, the foreign substances areforced in between the sliding surfaces, and flaws arisen between theshoe 76 and the sliding surface of the swash plate 60 is deepened. Sinceflaws arise easily, durability against foreign substances reduces.Consequently, sliding performance of the shoe 76 having a smallchamfered surface angle α is relatively low.

[0052] Meanwhile, when the chamfered surface angle α is too large, thatis, the chamfered surface angle α is closer to 90°, a problem onmanufacturing a shoe rises. A hemispherical crown shoe is generallymanufactured by flop forging. For example, a pair of dies for forgingthe shoe is constituted of a die for mainly molding the plane slidingsurface 136 and a die for mainly molding the spherical sliding surface138. A raw material in a predetermined shape plastically flows byforging the raw material in a cavity defined between the pair of dies.When forging by utilizing such the pair of dies, the accuracy of theheight of the hemispherical crown shoe is especially important, that is,the accuracy of a distance between the plane sliding surface 136 and thespherical sliding surface 138 is important. Therefore, the cavity ispreferably defined so as to permit quantity differentials among the rawmaterials at a side portion of the cavity. However, when the chamferedsurface angle α is too large, it is difficult to define a cavity forsufficiently permitting quantity differentials among the raw materialsat a side portion of the cavity. Thereby, the shoe having high accuracyis hardly forged. Therefore, a relatively small chamfered surface angleα of the shoe efficiently permits quantity differentials among the rawmaterials. When a shoe is inaccurately molded by forging, it takes manyhours to adjust the accuracy by polishing after forging. Thereby,manufacturing cost of the shoe increases. Therefore, a relatively smallchamfered surface α is desirable when a hemispherical crown shoe ismanufactured with low cost with high accuracy. Besides, when the heightof the shoe is inaccurate and a distance between the shoe and the pistonis relatively large, foreign substances are easily involved in betweenthe sliding surfaces, or when a distance between the shoe and the pistonis relatively small, friction generated between the sliding surfaces isexcessive. In either case, sliding performance deteriorates. Also, whenthe chamfered surface angle is 30° or above, characteristics forexcluding foreign substance further improves. Additionally, when thechamfered surface angle is 40° or above, characteristics for excludingforeign substance much further improves.

[0053] One of the manufacturing processes of the shoe 76 in the presentembodiment will be described. The shoe 76 is manufactured by the stepsof: a partially molding process, a forging process, a heat treatmentprocess, a grinding and polishing process, a plating process, and afinishing process. The base member 152 is formed by the steps of asemi-molding process, a forging process, a heat treatment process, and agrinding and polishing process. The metal plating layer 154 is formed bythe step of a plating process. The raw material of the shoe 76 will bedescribed first, and each of the manufacturing processes will bedescribed later.

[0054] The raw material of the base member 152 is a cylindrical aluminumseries alloy having a smaller diameter and a greater height than thebase member 152 of the shoe 76. The raw material is made by the steps ofmolding a billet, which is made of aluminum alloy with predeterminedcomposition, forming a cylindrical rod with a predetermined diameter byextruding and drawing the billet, annealing the cylindrical rod, cuttingthe cylindrical rod into pieces with predetermined length by a sawingmachine, and smoothing a surface of the cut raw material by barrelpolishing.

[0055] A part of the raw material is molded upon the partially moldingprocess. Particularly, the recess 142 at the center of the plane slidingsurface 136 of the shoe 76 is formed. The partially molding process isschematically shown in FIG. 7. A pressing apparatus with a pair of dies178 is used for partially molding the raw material. The pair of dies 178includes a drag 174 and a punch 176. The drag 174 forms a hole 172 witha bottom at one end, the hole 172 having approximately the same innerdiameter as the outer diameter of the raw material 170. The punch 176 isoperative to extend into the hole 172. The partially molding isperformed by the steps of putting the raw material 170 in the hole 172,forcing the end of the punch 176 onto the raw material 170, pushing theend of the punch 176 into the raw material 170 by moving the punch 176downward until the punch 176 reaches a predetermined position, A holebored by the end of the punch 176 forms the shape of the recess 142 ofthe base member 152.

[0056] The partially molded raw material is forged upon the forgingprocess. The forging process is schematically shown in FIG. 8. A forgingapparatus with a pair of dies 184 including a cope 180 and a drag 182 isused for cold-forging the partially molded raw material. The pair ofdies 184 defines a cavity, which has substantially the same shape as thebase member 152 of the shoe 76, by fitting the cope 180 onto the drag182. The drag 182 has a protrusion 186, the shape of which issubstantially the same shape as the recess 142. The partially molded rawmaterial 188 is positioned on the drag 182 by fitting the protrusion 186into the recess 142. In this manner, since the recess 142 is previouslyformed before a forging process, the partially molded raw material 188is positioned appropriately in the pair of dies 184 by means of therecess 142 and the protrusion 186. Thereby, the partially molded rawmaterial 188 plastically flows isotropically. The forged base members152 of the shoes 76 maintain substantially the same shape andapproximately the same dimensions, and ensure high quality. Afterputting the partially molded raw material 188 on the drag 182, the basemember 152 is forged by operating the cope 180 downward and fitting thecope 180 onto the drag 182.

[0057] More particularly, a plane portion 190 of a molding surface ofthe drag 182 molds a part of the base member 152 corresponding to theplane sliding surface 136 of the shoe 76, and an inclined portion 192 ofthe molding surface of the drag 182 molds a part of the base member 152corresponding to the chamfered surface 146. Therefore, an angle betweenthe plane portion 190 and the inclined portion 192 determines theforegoing chamfered surface angle α. A rounded corner 194 providedbetween the plane portion 190 and the inclined portion 192 determinesthe radius of curvature of the rounded corner 150 of the shoe 76.Likewise, a molding surface 196 of the cope 180 molds a part of the basemember 152 corresponding to the spherical sliding surface 138 of theshoe 76. The height of the base member 152 is determined by a clearancebetween the plane portion 190 of the drag 182 and the molding surface196 of the cope 180 upon fitting the cope 180 onto the drag 182.

[0058] The height of the hemispherical crown shoe is required to beaccurate, nevertheless. Quantity of the raw material 188 does not affectthe height of the forged base member 152. The volume of the cavity inthe pair of dies 184 is determined so as to exceed the volume of thepartially molded raw material 188. Thereby, the plastically flowed rawmaterial 188 does not fill the cavity, but flows toward the outerperiphery of the cavity. Then, a space 198 is left between theplastically flowed raw material 188 and the pair of dies 184. In otherwords, the rounded surface 148 of the side surface 140 is moldedsubstantially by open die forging, and the shape of the rounded surface148 reflects the quantity of the raw material 188. The plane slidingsurface 136, the spherical sliding surface 138 and the chamfered surface146 of the side surface 140 are accurately molded. In the presentembodiment, since the chamfered surface angle α of the shoe 76 is 45°,the volume of the space 198 become relatively large. Therefore, even ifthe quantity of each of the raw materials is different, the rawmaterials can accurately be forged. Accordingly, cost for adjusting thedimensions of the raw material reduces. As a result, manufacturing costof the shoe 76 reduces. For example, as the chamfered surface angle αincreases, the volume of the space 198 reduces. In such a state, apermissible range of the dimensions of the raw materials reduces.Therefore, the chamfered surface angle α may be preferably 60° or below,and more preferably be 50° or below.

[0059] In the present manufacturing process, the forging process isconstituted by only one process. However, a multi-process, whichincludes a plurality of sub-forging processes, may constitute theforging process. In such a state, the sub-molded raw material may betreated by annealing at one of intervals between the sub-forgingprocesses.

[0060] The base member 152 molded upon the forging process is treated bythermal refining upon the heat treatment process. In the presentembodiment, thermal refining treated to the base member 152 is T6treatment, in which the base member 152 is treated by solution heattreatment, and then treated by artificial age hardening. In the solutionheat treatment, the base member 152 is kept in a heating furnace with atemperature of approximately 490° C. for approximately an hour, andafter that the base member 152 is rapidly cooled to a room temperature.In the artificial age hardening, the base member 152 is kept in theheating furnace with a temperature of approximately 180° C. forapproximately five hours. T7 treatment in place of T6 treatment may beapplied. In T7 treatment, the base member 152 may be treated by solutionheat treatment, is and then treated by stabilizing treatment. In such astate, after treated by the solution heat treatment in theabove-mentioned condition, the base member 152 may be kept in a heatingfurnace with a temperature of approximately 200° C. for approximatelyfive hours.

[0061] The base member 152 treated by thermal refining is ground andpolished for adjusting its dimensions and smoothing its surface upon thegrinding process. The grinding and polishing process is constituted of asurface grinding process and a barrel polishing process. The surface ofthe base member 152 corresponding to the plane sliding surface 136 isground upon the surface grinding process. Several pieces of the basemembers 152 are aligned, and then ground by a surface grinding apparatusby means of free abrasive grains. The entire surface of the base member152 is polished upon the barrel polishing process. The base member 152together with free abrasive grains is put in a barrel polishingapparatus, and then is started. The surface grinding is mainly intendedto adjust the height of the base member 152. On the other hand, thebarrel polishing is mainly intended to smooth the surface of the basemember 152. The surface grinding process or the barrel polishingprocess, whichever can be performed first.

[0062] The surface of the polished base member 152 is coated with ametal plating layer upon the plating process. The metal plating layer isformed by electroless plating with nickel. An inner layer is formed byNi—P electroless plating, and then an outer layer is formed by Ni—P—B—Welectroless plating. The inner and the outer layers are formed by aconventional procedure, that is, the base member 152 is pretreated andthen immersed in a plating bath in accordance with the procedure.

[0063] The base member 152, the surface of which is coated with themetal plating layer 154, or the shoe 76, is polished upon the finishingprocess. The shoe 76 is ground by barrel polishing upon the finishingprocess. When necessary, the shoe 76 is treated by surface grinding.After that, the shoe 76 is polished by buffing. The barrel polishing andthe surface grinding are performed in such a manner as described aboveupon the grinding and polishing process. Since the shoes 76 abut againsteach other upon barrel polishing, when corners or substantially cornersare formed on the surfaces of the shoes 76, the shoes 76 can be flaweddue to the corners. Also, the metal plating layer 154 formed on thecorners may abrade, and the base members 152 could expose themselvesoutside. However, In the shoe 76 in the present embodiment, since aportion between the chamfered surface 146 and the plane sliding surface136 is the rounded corner 150, the radius of curvature of which is 0.2mm, the shoes 76 are inhibited from being flawed, and the metal platinglayers 154 are also inhibited from abrading.

[0064] The hemispherical crown shoe 76 is completed through theabove-described processes. Manufacturing processes are not limited tothe above-described processes. The shoe may be manufactured by variouskinds of processes in accordance with specifications of target shoes.

[0065] According to the present invention, the following advantageouseffects are obtained.

[0066] Since the strength of the lubricant layer is relatively low, thelubricant layer may be easily peeled off due to foreign substancesinvolved in between the shoes and the swash plate, and due to flaws ofthe shoes, however. In the present embodiment, the shoes 76 efficientlyexclude the foreign substances. Thereby, the shoes 76 are inhibited frombeing flawed. Accordingly, the shoes 76 rarely flaw the lubricant layerof the swash plate 60, and relatively high sliding performance lastsrelatively for a long time.

[0067] The present invention is not limited to the embodiment describedabove, but may be modified into the following examples.

[0068] For example, the present invention may be applied to a swashplate type compressor with a double-headed piston, having two heads onboth sides of the engaging portion relative to the swash plate, or maybe applied to a fixed displacement compressor.

[0069] In the shoe 76 in the present embodiment, the side surface 140includes the chamfered surface 146 and the rounded surface 148connecting with the chamfered surface 140. The side surface 140 in thepresent embodiment may be modified into structures shown in FIGS. 6A and6B. The side surface 140 of the shoe 76 shown in FIG. 6A includes only achamfered surface 146. Namely, the chamfered surface 146 connects withboth the plane sliding surface 136 and the spherical sliding surface138. The side surface 140 of the shoe 76 shown in FIG. 6B includes achamfered surface 146 and a cylindrical surface 168. Namely, one end ofthe chamfered surface 146 connects with the outer periphery of the planesliding surface 136, and the other end of the chamfered surface 146connects with one end of the cylindrical surface 168. In addition, theother end of the cylindrical surface 168 connects with the outerperiphery of the spherical sliding surface 138. Thus, the shape of theside surface 140 may be modified diversely. Besides, the shape of thesurface other than the chamfered surface is not limited. Only when theside surface of the shoe has the chamfered surface adjacent to the planesliding surface, the shoe may be applied. For example, the shoe havingthe chamfered surface connecting with the spherical sliding surface,that is, the entire of side surface is the chamfered surface, may beapplied. Also, for example, the side surface other than the chamferedsurface may form a cylindrical surface or a truncated cone-shapedsurface, and an angle between the side surface other than the chamferedsurface and the extended plane sliding surface may be optional, and thenthe side surface other than the chamfered surface may interconnect thechamfered surface and the spherical sliding surface. Also, the sidesurface other than the chamfered surface may include a plurality ofrounded surfaces, and each of the rounded surfaces has the differentradius of curvature.

[0070] An experiment is performed on the chamfered surface angle, theradius of curvature of the rounded corner and flaws of the shoes. Basedon the above-described spherical shoe, several shoes were manufacturedin such a manner that each of the chamfered surface angles was differentfrom one another. Additionally, a shoe having a conventional shape isalso manufactured. Each of the shoes was checked how the plane slidingsurface worked relative to cast iron particles. The test comparativelychecks characteristics for excluding cast iron particles and durabilityagainst cast iron particles. Manufactured shoes, conditions of thedurability test against cast iron particles, and results of thedurability test will now be described.

[0071] Five kinds of shoes in different shapes were manufactured. Theshoes were, respectively, numbered from #1 to #5. The shapes of themanufactured shoes are schematically shown in FIG. 9. Each of the shoes#1 to #5 has the same material of the base member, the same material ofthe metal plating layer formed on the surface, and the same thickness ofthe layer as those of the shoe is 76 described above.

[0072] The shoe #1 has a conventional shape. The shape of shoe #1 ispartially shown in FIG. 9A. An angle between the plane sliding surface136 and the extended surface 144 of the chamfered surface 146, or achamfered surface angle α1, is 10°, relatively small. The radius ofcurvature R1 of the rounded corner between the plane sliding surface 136and the chamfered surface 146 is 0.7 mm. A space 162, the cross sectionof which is wedge-shaped, is defined between the chamfered surface 146and the sliding surface of the swash plate, that is, between thechamfered surface 146 and the extended surface 144 in FIG. 9A. Theheight h1 of the outer periphery of the space 162 from the extendedsurface 144 is 0.16 mm.

[0073] The shoes #2 to #4 are the shoes according to the presentinvention. The shapes of shoes are partially shown in FIG. 9B. Thechamfered surface angles α 2 of the shoes #2 to #4 are, respectively,45°, 60°and 70°. Namely, each of the chamfered surface angles α2 of theshoes #2 to #4 is greater than the chamfered surface angle α1 of theshoe #1. The radiuses of curvature R2 of the corners R between the planesliding surfaces 136 and the chamfered surfaces 146 of the shoes #2 to#4 are all 0.2 mm. The similar spaces 162, the cross sections of whichare wedge-shaped, are also defined between the chamfered surfaces 146and the sliding surfaces of the swash plates, that is, between thechamfered surfaces 146 and the extended surfaces 144 in FIG. 9B. Theheights h2 of the outer peripheries of the spaces 162 for the shoes #2to #4 are, respectively, 0.67 mm, 0.82 mm and 0.89 mm.

[0074] The shoe #5 has a characteristic shape for being compared withthe other shoes #1 to #4. The shape of shoe #5 is partially shown inFIG. 9C. The shoe #5 has no chamfered surface, so that an angle α3between the side surface 140 and the extended surface 144 of the planesliding surface 136 is 90°. Namely, an angle between the chamferedsurface and the extended surface 144 of the plane sliding surface 136 is90°, and the side surface 140, which is cylindrical in shape, isadjacent to the plane sliding surface 136. The radius of curvature R3 ofthe rounded corner between the side surface 140 and the plane slidingsurface 136 is approximately 0 mm. In other words, the rounded corner ofthe shoe #5 is edged.

[0075] Upon the durability test, the above-described shoes #1 to #5 wereactually slid with respect to a swash plate. The durability test wasperformed in a manner shown in FIG. 10. An apparatus 210 for thedurability test includes a rotatable swash plate 60 and a shoe holder212, by which the shoes 76 are positioned on a sliding surface 132 ofthe swash plate 60 so as to slide with respect to the sliding surface132. The shoe holder 212 slidably holds the spherical sliding surface ofthe shoe 76, and slides the plane sliding surface of the shoe 76 withrespect to the sliding surface 132 of the swash plate 60. The shoeholder 212 also pushes the shoe 76 onto the swash plate 60 withpredetermined force. The swash plate 60 is the same as that in apractical use. The material of the base member, the thickness of thealuminum spraying layer formed on the sliding surface 132, a kind andthe thickness of a lubricant layer are the same as thosedescribed-above.

[0076] The swash plate 60 was rotated once on condition that the slidingsurface 132 of the swash plate 60 was lubricated by lubricant oil 50 μlamount, each of the shoes #1 to #5 was held by the shoe holder 212 andwas forced onto the swash plate 60 with force 784N, and cast ironparticles 10 mg in weight were scattered on all over the sliding surface132. The cast iron particles are classified into two types by diametersof the particles. One type is the particles having the diameter of 38 μmto 75 μm, and the other type is the particles having the diameter of 75μm to 120 μm. Each of the shoes #1 to #5 was tested with each type ofthe particles. Each of the shoes #1 to #5 was checked after the swashplate was rotated, and was scored by the number of flaws on the planesliding surface of the shoes 76 and by the depth of the deepest flaw.Additionally, the number of the flaws was visually checked, and thedepth of the flaw was checked by roughnessmeter.

[0077] The following TABLE 1 indicates the number of the flaws and thedepth of the deepest flaw on each of the shoes #1 to #5 in associatedwith the chamfered surface angle α and the rounded corner of each of theshoes #1 to #5 based on a result of the durability test for cast ironparticles of each type. Also, FIG. 11 is a graph showing the number ofthe flaws and the depth of the deepest flaw upon testing for cast ironparticles having the diameter of 38 μm to 75 μm. FIG. 12 is a graphshowing the number of the flaws and the depth of the deepest flaw upontesting for cast iron particles having the diameter of 75 μm to 120 μm.TABLE 1 RADIUS OF CURVATURE DIAMETER OF CAST DIAMETER OF CAST CHAMFEREDOF IRON PARTICLES IRON PARTICLES SURFACE ROUNDED 38 to 75 (μm) 75 to 120(μm) SHOE ANGLE α CORNER NUMBER DEEPEST NUMBER DEEPEST No. (°) (mm) OFFLAWS FLAW (μm) OF FLAWS FLAW (μm) #1 10 0.7 25 1.9 20 4.0 #2 45 0.2 70.8 2 0.4 #3 60 0.2 4 0.7 4 0.9 #4 70 0.2 10 0.9 3 0.9 #5 90 0 1 0.8 21.5

[0078] As shown in TABLE 1, FIGS. 11 and 12, the shoe #1, the chamferedsurface angle α of which is relatively small 10°, has the greatestnumber of flaws and the deepest depth of flaw, irrespective of thediameter of the particles. Meanwhile, the shoes #2 to #4, the chamferedsurface angles α of which are relatively large, have the fewer number offlaws and the shallower depth of flaws than those of the shoe #1.Particularly, particles having relatively large diameter cause thesliding surfaces of the shoe and the swash plate to be flawed, anddeteriorate sliding performance between the sliding surfaces. Therefore,particles having relatively large diameter are simulated by scatteringparticles of diameter 75 μm to 120 μ. The test result indicates thatdifferentials of the number of flaws and the depth of the deepest flawbetween the shoe #1 and the shoes #2 to #4 are relatively large.Accordingly, the shoes #2 to #4 having relatively large chamferedsurface angle α efficiently exclude the cast iron particles, and ensurerelatively high durability against the cast iron particles. Thereby, itwas demonstrated that the shoe 76 in the present embodiment ensuresrelatively high sliding performance.

[0079] Besides, the shoe #5 having no chamfered surface but edged corneris manufactured for being compared with the other shoes #1 to #5. Theshoe #5 as well as the shoes #2 to #4 efficiently excludes the cast ironparticles and ensures relatively high durability against the cast ironparticles. However, there is difficulty in accurately manufacturing ashoe with low cost. Additionally, the edged corner may cause the slidingsurface of the swash plate to be flawed. Therefore, the shoe #5 is notpractical.

[0080] Therefore, the present examples and embodiments are to beconsidered as illustrative and not restrictive and the invention is notto be limited to the details given herein but may be modified within thescope of the appended claims.

What is claimed is:
 1. A shoe interposed between a swash plate and apiston in a swash plate type compressor, the shoe comprising: a planesliding surface, which is substantially a plane, sliding with respect tothe swash plate; a spherical sliding surface, which is substantially apart of sphere surface, sliding with respect to the piston; and a sidesurface between the plane sliding surface and the spherical slidingsurface, the side surface including a chamfered surface adjacent to theplane sliding surface; wherein an angle between the chamfered surfaceand the extended plane sliding surface ranges from 20° to 80°.
 2. Theshoe according to claim 1, wherein the angle between the chamferedsurface and the extended plane sliding surface is 30° or above.
 3. Theshoe according to claim 2, wherein the angle between the chamferedsurface and the extended plane sliding surface is 40° or above.
 4. Theshoe according to claim 1, wherein the angle between the chamferedsurface and the extended plane sliding surface is 60° or below.
 5. Theshoe according to claim 4, wherein the angle between the chamferedsurface and the extended plane sliding surface is 50° or below.
 6. Theshoe according to claim 1 further comprising: a rounded corner betweenthe chamfered surface and the plane sliding surface.
 7. The shoeaccording to claim 6, wherein the radius of the curvature of the roundedcorner is 0.05 mm or above.
 8. The shoe according to claim 7, whereinthe radius of the curvature of the rounded corner is 0.1 mm or above. 9.The shoe according to claim 8, wherein the radius of the curvature ofthe rounded corner is 0.15 mm or above.
 10. The shoe according to claim6, wherein the radius of the curvature of the rounded corner is 0.5 mmor below.
 11. The shoe according to claim 10, wherein the radius of thecurvature of the rounded corner is 0.4 mm or below.
 12. The shoeaccording to claim 11, wherein the radius of the curvature of therounded corner is 0.3 mm or below.
 13. The shoe according to claim 1further comprising: a base member made of aluminum series alloy.
 14. Theshoe according to claim 13, wherein at least a part of the surface ofthe base member is coated with metal plating layer.
 15. The shoeaccording to claim 1 further comprising: a base member made of ironseries alloy.
 16. A swash plate type compressor comprising: a housing; adrive shaft rotatably supported by the housing; a swash plateoperatively connected to the drive shaft; a piston accommodated in thehousing, the piston operatively connected to the swash plate; and a pairof shoes interposed between the swash plate and the piston, each of theshoes including: a plane sliding surface, which is substantially aplane, sliding with respect to the swash plate; a spherical slidingsurface, which is substantially a part of sphere surface, sliding withrespect to the piston; and a side surface between the plane slidingsurface and the spherical sliding surface, the side surface including achamfered surface adjacent to the plane sliding surface; wherein anangle between the chamfered surface and the extended plane slidingsurface ranges from 20° to 80°.
 17. The swash plate type compressoraccording to claim 16, wherein the swash plate includes a base membermade of iron series alloy.
 18. The swash plate type compressor accordingto claim 16, wherein the is swash plate includes lubricant layers onsurfaces sliding with respect to the shoes.
 19. The swash plate typecompressor according to claim 18, wherein the swash plate includes ametal spraying layer made of one of aluminum, copper and alloys of them,the metal spraying layer is formed on the surfaces sliding with respectto the shoes, and the lubricant layer is formed on the surface of themetal spraying layer.